It is known to add hydrazine compounds to silver halide photographic emulsions or developers. For example, a developer containing ascorbic acid and hydrazine is described in U.S. Pat. No. 3,730,727, the use of hydrazine as an auxiliary developing agent for obtaining direct positive color images is described in U.S. Pat. No. 3,227,552, a silver halide photographic material containing .beta.-monophenylhydrazide of an aliphatic carboxylic acid as a stabilizer thereof is described in U.S. Pat. No. 3,386,831, and other photographic techniques using hydrazine compounds are also described in U.S. Pat. No. 2,419,975 and Mees, The Theory of Photographic Process, 3rd edition, 281 (1966).
In particular, aforesaid U.S. Pat. No. 2,419,975 discloses that high contrast negative images can be obtained by the addition of hydrazine compounds. That is, it is described in the aforesaid patent that when a hydrazine compound is added to a silver chlorobromide emulsion and the emulsion is developed by a developer having high pH of 12.8, a very high contrast photographic property of over 10 in gamma (.gamma.) is obtained. However, such a high alkaline developer of pH near 13 is liable to be air-oxidized and thus is unstable, whereby the developer can not endure the storage or use thereof for a long period of time.
The high contrast photographic property of over 10 in gamma is very useful for the photographic reproduction of continuous tone images by dot images useful for making printing plate or the reproduction of line images. For such a purpose, a process of using a silver chlorobromide emulsion containing more than 50 mol %, preferably more than 75 mol % silver chloride and developing the emulsion layer with a hydroquinone developer having very low effective concentration of sulfite ion (usually lower than about 0.1 mol/liter) has been generally used. However, since in the process the sulfite ion concentration in the developer is low, the developer is very unstable and can not endure the storage over 3 days.
Furthermore, since the aforesaid process uses a silver chlorobromide emulsion having a relatively high content of silver chloride, a high sensitivity cannot be obtained. Accordingly, it has strongly been desired to obtain very high contrast photographic characteristics useful for the reproduction of dot images or line images using high-speed silver halide emulsions and a stable developer.
The inventors previously proposed silver halide photographic emulsions giving very high contrast negative gradation photographic characteristics using stable developers in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614, and 4,323,643 but have found that the acylhydrazine compounds disclosed in the patents have the following disadvantage.
That is, it is known that these hydrazines disclosed therein generate nitrogen gases during processing, these gases gather to form bubbles in the photographic material containing the compounds to spoil the photographic images formed, and further the compounds come out in a processing solution, which give bad influences on other photographic materials.
Also, these conventional hydrazines give greatly high contrast but at the same time cause undesirable phenomenon called as "black pepper" by infectious development, which is a large problem in photo-engraving process. The black pepper is black spots formed at the places to become undeveloped portions among, for example, dots. The occurrence of the black pepper increases when the photographic light-sensitive materials are stored for a long period of time at, in particular, high temperature and high humidity and also increases by the reduction of sulfite ions, which are generally used as preservatives, or by the increase of the pH value of a processing solution caused by the fatigue of the processing solution with the passage of time, which results in greatly reducing the commercial value of the photographic light-sensitive materials for photo-engraving.
Accordingly, for preventing the occurrence of the black pepper, various efforts have been made by the attempts for preventing the occurrence of black pepper are frequently accompanied by reduction of sensitivity and gamma. Thus, silver halide photographic materials giving less black peppers without the reduction in sensitivity and contrast have been desired.
Furthermore, in the case of these conventional hydrazines, a large amount thereof must be used for sufficiently increasing the sensitivity and contrast of the photographic light-sensitive materials and further when these hydrazines are used in combination with other sensitizing technique (e.g., a means of enhancing chemical sensitization, a means of increasing silver halide grain sizes, or a means of adding a compound capable of accelerating sensitization as described in U.S. Pat. Nos. 4,272,606 and 4,241,164) in the case of requiring a particularly high speed for photographic light-sensitive materials, the photographic materials undergo sensitization and fogging with the passage of time during storage thereof.
Accordingly, compounds which are freed from the generation of bubbles and coming out in processing solution as described above, give no problem on the stability of the photographic materials with the passage of time, and can provide very high contrast photographic characteristics with the addition of a very small amount thereof have been desired.
Also, it is described in U.S. Pat. Nos. 4,385,108 and 4,269,929 that very high contrast negative gradation photographic characteristics are obtained by using hydrazines having a substituent liable to adsorb on silver halide grains but the hydrazine compounds practically described in the examples of the aforesaid patents have a problem of causing desensitization with the passage of time during storage of the photographic light-sensitive materials containing them. Therefore, it is necessary to select compounds which do not cause the aforesaid problem.
On the other hand, there are various kinds of direct positive photographic processes and in these processes, a process comprising light-exposing photographic materials containing silver halide grains previously fogged and then developing the photographic materials in the presence of a desensitizer, and a process comprising light-exposing photographic materials having silver halide emulsion layer(s) having sensitivity specks mainly in the insides of the silver halide grains and developing the materials in the presence of a nucleating agent are most useful. The present invention relates to the latter type process.
A silver halide emulsion having sensitive specks mainly in the insides of the silver halide grains thereof and forming latent images mainly in the insides of the silver halide grains is called internal latent image type silver halide emulsion, which is distinguished from a silver halide emulsion forming latent images mainly on the surfaces of the silver halide grains thereof.
Processes of obtaining direct positive images by surface-developing the internal latent image-type silver halide photographic emulsions in the presence of a nucleating agent and photographic emulsions or photographic light-sensitive materials which are used in such processes are described, for example, in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318, 3,227,552, 3,317,322, British Patents 1,011,062, 1,151,363, 1,269,640, 2,011,391, Japanese Patent Publication Nos. 29405/68, 38164/74, Japanese Patent Application (OPI) Nos. 16623/78, 137133/78, 37732/79, 40629/79, 74536/79, 74729/79, 52055/80, and 90940/80 (the term "OPI" as used herein indicates an "unexamined published application").
In the aforesaid process of obtaining direct positive images, the nucleating agent may be added to a developer but when the nucleating agent is added to the silver halide photographic emulsion layer(s) or other proper layer(s) of photographic light-sensitive materials to adsorb it on the surface of silver halide grains, better reversal characteristics can be obtained.
As the nucleating agent which is used for the aforesaid process of obtaining direct positive images, there are hydrazines described in U.S. Pat. Nos. 2,563,785 and 2,588,982, hydrazine and hydrazine series compounds described in U.S. Pat. No. 3,227,552, heterocyclic quaternary salt compounds described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738, 4,094,683 and 4,115,122, British Patent 1,283,835, Japanese Patent Application (OPI) Nos. 3426/77 and 69613/77, thiourea combined type acylphenylhydrazine series compounds described in U.S. Pat. Nos. 4,030,925, 4,031,127, 4,139,387, 4,245,037, 4,255,511 and 4,276,364, and British Patent 2,012,443, compounds having a heterocyclic thioamide as adsorptive group described in U.S. Pat. No. 4,080,207, phenylacylhydrazine compounds including a heterocyclic group having a mercapto group as adsorptive group described in British Patent 2,011,397B, sensitizing dyes having a substituent showing a nucleating action in the molecular structure described in U.S. Pat. No. 3,718,470, and hydrazine compounds described in Japanese Patent Application (OPI) Nos. 200230/84, 212828/84 and 212829/84 and Research Disclosure, No. 23510 (November, 1983).
However, these compounds have such disadvantages that they are insufficient in activity as nucleating agent or some of those having high activity as nucleating agent are insufficient in storage stability, the activity thereof varies even before coating a silver halide emulsion to which the compound has been added, and further when a large amount of the compound is added to a silver halide emulsion, the layer quality of the emulsion layer is reduced.